From fd1c7e131f331942d20f42f31e79912d570081fa Mon Sep 17 00:00:00 2001 From: "djm@openbsd.org" Date: Thu, 2 Apr 2026 07:48:13 +0000 Subject: [PATCH] upstream: correctly match ECDSA signature algorithms against algorithm allowlists: HostKeyAlgorithms, PubkeyAcceptedAlgorithms and HostbasedAcceptedAlgorithms. Previously, if any ECDSA type (say "ecdsa-sha2-nistp521") was present in one of these lists, then all ECDSA algorithms would be permitted. Reported by Christos Papakonstantinou of Cantina and Spearbit. OpenBSD-Commit-ID: c790e2687c35989ae34a00e709be935c55b16a86 --- auth2-hostbased.c | 9 +++++---- auth2-pubkey.c | 9 +++++---- auth2-pubkeyfile.c | 26 +++++++++++++++----------- sshconnect2.c | 28 ++++++++++++++++++---------- 4 files changed, 43 insertions(+), 29 deletions(-) diff --git a/auth2-hostbased.c b/auth2-hostbased.c index e2ed8b3eb..8a1acdec3 100644 --- a/auth2-hostbased.c +++ b/auth2-hostbased.c @@ -1,4 +1,4 @@ -/* $OpenBSD: auth2-hostbased.c,v 1.56 2025/12/22 01:49:03 djm Exp $ */ +/* $OpenBSD: auth2-hostbased.c,v 1.57 2026/04/02 07:48:13 djm Exp $ */ /* * Copyright (c) 2000 Markus Friedl. All rights reserved. * @@ -96,9 +96,10 @@ userauth_hostbased(struct ssh *ssh, const char *method) error_f("cannot decode key: %s", pkalg); goto done; } - if (key->type != pktype) { - error_f("type mismatch for decoded key " - "(received %d, expected %d)", key->type, pktype); + if (key->type != pktype || (sshkey_type_plain(pktype) == KEY_ECDSA && + sshkey_ecdsa_nid_from_name(pkalg) != key->ecdsa_nid)) { + error_f("key type mismatch for decoded key " + "(received %s, expected %s)", sshkey_ssh_name(key), pkalg); goto done; } if (match_pattern_list(pkalg, options.hostbased_accepted_algos, 0) != 1) { diff --git a/auth2-pubkey.c b/auth2-pubkey.c index be378f266..e446ef412 100644 --- a/auth2-pubkey.c +++ b/auth2-pubkey.c @@ -1,4 +1,4 @@ -/* $OpenBSD: auth2-pubkey.c,v 1.125 2025/12/22 01:49:03 djm Exp $ */ +/* $OpenBSD: auth2-pubkey.c,v 1.126 2026/04/02 07:48:13 djm Exp $ */ /* * Copyright (c) 2000 Markus Friedl. All rights reserved. * Copyright (c) 2010 Damien Miller. All rights reserved. @@ -148,9 +148,10 @@ userauth_pubkey(struct ssh *ssh, const char *method) error_f("cannot decode key: %s", pkalg); goto done; } - if (key->type != pktype) { - error_f("type mismatch for decoded key " - "(received %d, expected %d)", key->type, pktype); + if (key->type != pktype || (sshkey_type_plain(pktype) == KEY_ECDSA && + sshkey_ecdsa_nid_from_name(pkalg) != key->ecdsa_nid)) { + error_f("key type mismatch for decoded key " + "(received %s, expected %s)", sshkey_ssh_name(key), pkalg); goto done; } if (auth2_key_already_used(authctxt, key)) { diff --git a/auth2-pubkeyfile.c b/auth2-pubkeyfile.c index 896ea1996..e729cc50a 100644 --- a/auth2-pubkeyfile.c +++ b/auth2-pubkeyfile.c @@ -1,4 +1,4 @@ -/* $OpenBSD: auth2-pubkeyfile.c,v 1.7 2025/12/22 01:49:03 djm Exp $ */ +/* $OpenBSD: auth2-pubkeyfile.c,v 1.8 2026/04/02 07:48:13 djm Exp $ */ /* * Copyright (c) 2000 Markus Friedl. All rights reserved. * Copyright (c) 2010 Damien Miller. All rights reserved. @@ -50,6 +50,7 @@ #include "authfile.h" #include "match.h" #include "ssherr.h" +#include "xmalloc.h" int auth_authorise_keyopts(struct passwd *pw, struct sshauthopt *opts, @@ -146,20 +147,23 @@ auth_authorise_keyopts(struct passwd *pw, struct sshauthopt *opts, static int match_principals_option(const char *principal_list, struct sshkey_cert *cert) { - char *result; + char *list, *olist, *entry; u_int i; - /* XXX percent_expand() sequences for authorized_principals? */ - - for (i = 0; i < cert->nprincipals; i++) { - if ((result = match_list(cert->principals[i], - principal_list, NULL)) != NULL) { - debug3("matched principal from key options \"%.100s\"", - result); - free(result); - return 1; + olist = list = xstrdup(principal_list); + for (;;) { + if ((entry = strsep(&list, ",")) == NULL || *entry == '\0') + break; + for (i = 0; i < cert->nprincipals; i++) { + if (strcmp(entry, cert->principals[i]) == 0) { + debug3("matched principal from key i" + "options \"%.100s\"", entry); + free(olist); + return 1; + } } } + free(olist); return 0; } diff --git a/sshconnect2.c b/sshconnect2.c index e4f5bd0fd..478a9a52f 100644 --- a/sshconnect2.c +++ b/sshconnect2.c @@ -1,4 +1,4 @@ -/* $OpenBSD: sshconnect2.c,v 1.384 2026/03/03 09:57:25 dtucker Exp $ */ +/* $OpenBSD: sshconnect2.c,v 1.385 2026/04/02 07:48:13 djm Exp $ */ /* * Copyright (c) 2000 Markus Friedl. All rights reserved. * Copyright (c) 2008 Damien Miller. All rights reserved. @@ -85,6 +85,7 @@ extern Options options; static char *xxx_host; static struct sockaddr *xxx_hostaddr; static const struct ssh_conn_info *xxx_conn_info; +static int key_type_allowed(struct sshkey *, const char *); static int verify_host_key_callback(struct sshkey *hostkey, struct ssh *ssh) @@ -94,6 +95,10 @@ verify_host_key_callback(struct sshkey *hostkey, struct ssh *ssh) if ((r = sshkey_check_rsa_length(hostkey, options.required_rsa_size)) != 0) fatal_r(r, "Bad server host key"); + if (!key_type_allowed(hostkey, options.hostkeyalgorithms)) { + fatal("Server host key %s not in HostKeyAlgorithms", + sshkey_ssh_name(hostkey)); + } if (verify_host_key(xxx_host, xxx_hostaddr, hostkey, xxx_conn_info) != 0) fatal("Host key verification failed."); @@ -1598,34 +1603,37 @@ load_identity_file(Identity *id) } static int -key_type_allowed_by_config(struct sshkey *key) +key_type_allowed(struct sshkey *key, const char *allowlist) { - if (match_pattern_list(sshkey_ssh_name(key), - options.pubkey_accepted_algos, 0) == 1) + if (match_pattern_list(sshkey_ssh_name(key), allowlist, 0) == 1) return 1; /* RSA keys/certs might be allowed by alternate signature types */ switch (key->type) { case KEY_RSA: - if (match_pattern_list("rsa-sha2-512", - options.pubkey_accepted_algos, 0) == 1) + if (match_pattern_list("rsa-sha2-512", allowlist, 0) == 1) return 1; - if (match_pattern_list("rsa-sha2-256", - options.pubkey_accepted_algos, 0) == 1) + if (match_pattern_list("rsa-sha2-256", allowlist, 0) == 1) return 1; break; case KEY_RSA_CERT: if (match_pattern_list("rsa-sha2-512-cert-v01@openssh.com", - options.pubkey_accepted_algos, 0) == 1) + allowlist, 0) == 1) return 1; if (match_pattern_list("rsa-sha2-256-cert-v01@openssh.com", - options.pubkey_accepted_algos, 0) == 1) + allowlist, 0) == 1) return 1; break; } return 0; } +static int +key_type_allowed_by_config(struct sshkey *key) +{ + return key_type_allowed(key, options.pubkey_accepted_algos); +} + /* obtain a list of keys from the agent */ static int get_agent_identities(struct ssh *ssh, int *agent_fdp,